A polybutylene terephthalate (PBT)-series resin is excellent in various properties such as heat resistance, chemical resistance, electric properties, mechanical properties and shaping processability (or moldability), and is used for a number of applications. Specific examples of the applications include a variety of automotive electrical components or parts (e.g., various control units, various sensors, and ignition coils), connectors, switch parts, relay parts, and coil parts. These components or parts sometimes need airtightness, and in order to produce such components or parts conveniently, bonding (or joining) means such as an adhesive, a hot plate welding, and an ultrasonic welding have been utilized. Regarding these bonding means, however, some problems have been pointed out. For example, in the case of using an adhesive, the waste of process time up to curing of the adhesive, or the burden on the environment becomes an issue. Moreover, in a hot plate welding or an ultrasonic welding, there is fear that a product receives a damage due to heat, vibration, and others.
On the other hand, a bonding (or joining) method by a laser welding has no damage of a product due to heat or vibration involved in the welding, and the welding process is also very simple. However, it is pointed out that, in the case of bonding a PBT-series resin by a laser welding, the resin cannot be substantially welded because of carbonization or others due to a low transmission of a laser beam. Japanese Patent Application Laid-Open No. 26656/2001 (JP-2001-26656A: Patent Document 1) discloses a process for producing a united molded product which comprises uniting a molded product formed from a polyester-series copolymer having a melting point within a specific range with other molded product by welding processing. This document describes that a homopolyalkylene arylate resin (a polybutylene terephthalate, a polyethylene terephthalate, and a polyethylene naphthalate) has a low laser welding strength.
Japanese Patent Application Laid-Open No. 245481/1998 (JP-10-245481A: Patent Document 2) discloses a thermoplastic resin composition which comprises a composition composed of a thermoplastic polycarbonate resin and a thermoplastic polyester resin (such as a polyethylene terephthalate) and a methacrylic ester-series resin (graft resin) blended therewith in a proportion of 1 to 10% by weight, in which the methacrylic ester-series resin is obtained by graft-polymerizing a monomer containing a methacrylic ester as a main component in the presence of a crosslinked acrylic ester-series elastic body. This document mentions an embodiment in which a bisphenol A-based polycarbonate resin and a polyethylene terephthalate resin are used in a proportion of 1.5/1 to 4/1 (weight ratio) in the resin composition. Further, as a heat-welding method of the resin composition, a hot plate welding, a vibration welding or an ultrasonic welding is also described. In this composition, however, it is necessary to use the graft resin in order to improve welding strength of the composition, and the use of the graft resin tends to deteriorate mechanical strength, heat resistance or others of the composition.
Further, according to a molded product comprising a PBT-series resin as a base, a transmittance relative to a laser beam sometimes fluctuates depending on the site to be irradiated. Therefore, in the case where such a molded product is bonded to a counterpart material (or a resin molded product (or a molded product formed from a resin)) through a welding by a laser beam, it is sometimes impossible to weld the molded product and the counterpart molded product uniformly and firmly with each other on the contact interface.    [Patent Document 1] JP-2001-26656A (Claims)    [Patent Document 2] JP-10-245481A (Claims)